1. Field of the Invention
The present invention relates to a laminated inductor constructed using a laminated ceramic integral firing technique, and a method of producing the same, and more particularly, to a laminated inductor in which a low dielectric constant material layer is arranged between conductor patterns defining a coil conductor, and a method of producing the same.
2. Description of the Related Art Conventionally, laminated inductors using magnetic ceramics have been widely used. FIGS. 8 and 9 are a cross-sectional view and a perspective view, respectively, showing a conventional laminated inductor.
A laminated inductor 51 includes a sintered ceramic body 52 made of a magnetic ceramic material. A coil conductor 53 is embedded inside of the sintered ceramic body 52. The coil conductor 53 defines a spiral winding circuit inside of the sintered ceramic body 52. One end portion 53a extends to an end surface 52a, while the other end portion 53b extends to an end surface 52b. Terminal electrodes 54 and 55 are arranged to cover the ends surfaces 52a and 52b, respectively. Thus, the coil conductor 53 is connected to the terminal electrodes 54 and 55.
In order to manufacture the above-described sintered ceramic body 52, conductor patterns constituting a coil pattern are printed on magnetic green sheets, respectively. A plurality of magnetic green sheets each having a conductor pattern printed thereon are laminated, and then magnetic green sheets having no conductor patterns thereon are laminated on the upper side and the lower side of the laminated magnetic green sheets to define a laminated body. The laminated body is then fired so as to produce the sintered ceramic body 52. Thus, the sintered ceramic body 52 is formed by the well-known laminated ceramic integral firing technique.
Examples of the above-described conductor patterns will be described with reference to FIG. 9. FIG. 9 shows the uppermost conductor pattern 53c of the coil conductor 53 and the lower conductor pattern 53d. The conductor pattern 53c is printed on a magnetic green sheet 56. The end portion 53a of the conductor pattern 53c extends to one-side edge 56a of the magnetic green sheet 56. Further, a via-hole electrode 57 is located near the inner-side end portion of the conductor pattern 53c. 
A conductor pattern 53d is located on the upper side of a magnetic green sheet 58. The vicinity of one end portion 53d1 of the conductor pattern 53d is arranged so as to overlap with the via-hole electrode 57. That is, when the magnetic green sheets 56 and 58 are laminated, the conductor patterns 53c and 53d are electrically connected to each other through the via-hole electrode 57. A via-hole electrode 59 is formed in the vicinity of the other end of the conductor pattern 53d. The via-hole electrode 59 is electrically connected to a conductor pattern positioned below the conductor pattern 53d. In this manner, a plurality of conductor patterns are laminated through magnetic green sheets, respectively, to define the above-described coil conductor 53.
The laminated inductor 51 is produced by using the laminated ceramic integral firing technique. Accordingly, the control of the number of turns of the coil conductor 53 can be easily performed, and moreover, a small-sized inductance component can be formed.
However, since the conductor patterns at different heights or vertical positions in the coil conductor 53 overlap through magnetic ceramic layers, the generation of stray capacitances between the conductor patterns at the different vertical positions can not be prevented. For this reason, in the laminated inductor 51, the noise-removing characteristics are reduced, due to the effects of the above-described stray capacitances.
In order to overcome the problems described above, preferred embodiments of the present invention provide a laminated inductor in which stray capacitances between conductor patterns located at different vertical positions are minimized, and thereby, the noise-removing characteristic is greatly improved.
According to a preferred embodiment of the present invention, a laminated inductor includes a sintered ceramic body, and a coil conductor disposed inside of the sintered ceramic body which includes a sintered ceramic body made of a ceramic, a coil conductor disposed inside of the sintered ceramic body and including two ends which extend to the outer surface of the sintered ceramic body, first and second external electrodes located on the areas to which the coil conductor of the sintered ceramic body extend, respectively, the coil conductor including a plurality of conductor patterns located at different vertical positions in the sintered ceramic body, and a via-hole electrode through which conductor patterns, which are vertically adjacent to each other in the sintered ceramic body, are connected to each other, and low dielectric constant material layers laminated to both sides in the thickness direction of at least one of the plurality of conductor patterns, the low dielectric constant material having a lower dielectric constant than that of the ceramic constituting the sintered ceramic body.
Preferably, a first ring-path corresponding to one turn of the coil conductor is located in a height range where the conductor pattern is located. The first ring-path is defined by the conductor pattern and a low dielectric constant material layer. Also, a second ring-path corresponding to one turn of the coil conductor is defined by the via-hole electrode and a low dielectric constant material layer, and is located in the height range where a via-hole electrode is located.
Moreover, according to another preferred embodiment of the present invention, there is provided a method of producing a laminated inductor in which a coil conductor is located inside of a sintered ceramic body made of a ceramic material. The method includes the steps of preparing a first composite sheet having a conductor pattern defining a portion of the coil conductor and a low dielectric constant material pattern connected to the conductor pattern located on a support film, the conductor pattern and the low dielectric constant material pattern defining a ring-path corresponding to one turn of the conductor pattern, and a ceramic green layer provided on the support film excluding the area where the conductor pattern and the low dielectric constant material pattern are formed, preparing a second composite sheet including a via-hole electrode, a low dielectric constant material pattern formed so as to define together with the via-hole electrode a ring-path corresponding to one turn of the coil conductor, and a ceramic green layer provided on a support film excluding the area where the via-hole electrode and the low dielectric constant material pattern are formed, laminating the first and second composite sheets to each other with the support film between the composite sheets being released in such a manner that the conductor pattern of the first composite sheet overlaps the via-hole electrode of the second composite sheet, repeating the above-described lamination step to produce a laminate body in which a coil conductor including the plurality of conductor patterns and the via-hole electrode, and both ends of the coil conductor are exposed to the outer surface of the laminate body, firing the laminate body to produce a sintered ceramic body, and forming first and second external electrodes to be electrically connected to both ends of the coil conductor on the outer surface of the sintered ceramic body.
Preferably, in the method of producing a laminated inductor according to a preferred embodiment of the present invention, the conductor pattern is formed so as to have 1/n times the length of the ring-path, and in the step of laminating the plurality of first composite sheets through the second composite sheets, respectively, a first composite sheet at an upper position is rotated by about 360xc2x0 n relative to the center of the ring-path with respect to the next lower first composite sheet and then the first composite sheet is laminated on the next lower first composite sheet.
More preferably, in the method of manufacturing a laminated inductor according to a preferred embodiment of the present invention, the first and second composite sheets have a substantially rectangular plan shape, respectively, the conductor pattern constitutes about half the length of the ring-path, and in the step of laminating the plurality of first composite sheets through the second composite sheets, respectively, an upper first composite sheet is rotated by about 1800 relative to the center of the ring-path with respect to the next lower first composite sheet and then the upper first composite sheet is laminated on the next lower first composite sheet.
Other features, elements, characteristics and advantages of the present invention will become more apparent from detailed description of the preferred embodiments below.